The disclosure of Japanese Patent Application No. 11-329889 filed on Nov. 19, 1999, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an engine stopping/starting control apparatus and an engine stopping/starting control method employed in a vehicle in which the engine is stopped upon fulfillment of a predetermined stopping condition even if a shift position is a running position and in which the engine is started upon fulfillment of a predetermined starting condition.
2. Description of Related Art
In order to improve fuel consumption of a motor vehicle in response to a demand for conservation of resources, an apparatus which performs stopping/starting control of an engine during operation has been proposed. This apparatus is often employed in a so-called hybrid vehicle and the like. As will be described hereinafter, this apparatus temporarily stops the engine in a running state of the vehicle and thereafter restarts the engine.
FIG. 6 shows an example of a hybrid system 1 for a hybrid vehicle. The hybrid system 1 has an engine 2, a motor generator 6 coupled to a crank shaft of the engine 2, a transmission 4 coupled to an output shaft of the motor generator 6, a battery 8, and an inverter 10. The battery 8 and the inverter 10 exchange power with the motor generator 6.
The hybrid system 1 is a parallel hybrid system in which wheels can be driven by one or both of the engine 2 and the motor generator 6. If the wheels are driven only by the engine 2, the motor generator 6 functions as a dynamo. In this case, the vehicle can travel while charging the battery 8 through the inverter 10.
A stopping/starting control apparatus for the engine 2 employed in the hybrid system 1 is mainly realized through control performed by a controller 12. Even in the case where the shift position of the vehicle is a running position, the engine 2 is stopped upon fulfillment of a predetermined stopping condition and then restarted upon fulfillment of a predetermined starting condition. The controller 12 minimizes the operating period of the engine 2, and operates the engine 2 in its most efficient state, thereby improving fuel consumption and reducing concentrations of emission substances in comparison with a vehicle which is only equipped with an internal combustion engine. In addition, the apparatus eliminates restrictions on a traveling range or the trouble of external charging as in an electric vehicle whose wheels are driven only by a motor.
Conditions for stopping and restarting the engine 2 are determined, for example, from the sum of an electrical load (based on the driving of the motor generator 6, operation of an air-conditioner and the like) and a work by the wheels calculated from a depression amount of an accelerator pedal, a vehicle speed and the like (the sum will hereinafter be referred to as required power). If the required power has dropped below a threshold set as the stopping condition, the engine 2 is stopped. If the required power has exceeded a threshold set as the starting condition, the engine 2 is restarted.
As described above, if the engine 2 is stopped or started upon fulfillment of predetermined stopping/starting conditions even in the case where the shift position of the vehicle is a running position, the following problems may be caused.
For example, if the shift position of the vehicle is a running position and if the vehicle travels by being driven only by the motor generator 6 with the engine 2 out of operation, the engine 2 is restarted by the stopping/starting control apparatus upon fulfillment of a predetermined starting condition. Thus, oscillation of the vehicle resulting from the starting operation may adversely affect the driveability. Further, since a driving force of the engine 2 is added to a driving force of the motor generator 6, an acceleration shock (or a deceleration shock) may be sensed by the driver. Especially when the vehicle travels at a constant or low speed, the driver may keenly feel a sense of incongruity.
Furthermore, in the case where the vehicle speed is equal to zero (the vehicle is stopped) with the shift position being a running position, namely, where the brake has been depressed with the accelerator released, if the engine is restarted, the driver may sensitively respond to oscillation of the engine and feel a sense of incongruity. Further, a shock transmitted to the wheels in a stopped state of the vehicle may cause unpleasantness to the driver.
It is one object of the invention to mitigate to the utmost a sense of incongruity or unpleasantness caused to the driver by restarting an engine and to thereby improve the driveability of the vehicle.
In order to achieve the above-stated object, an engine control apparatus of one aspect of the invention includes a shift position detector that detects a shift position of a vehicle, and a controller. The controller stops the engine upon fulfillment of a stopping condition, and restarts the engine afterwards upon fulfillment of a first starting condition if the detected shift position is a running position and upon fulfillment of a second starting condition if the detected shift position is a non-running position.
In the aforementioned aspect of the invention, the first starting condition may make it more difficult to restart the engine than the second starting condition.
According to the aforementioned aspect of the invention, if the shift position is a running position, the engine is more unlikely to be started smoothly in comparison with the case where the shift position is a non-running position. Thus, the number of times for starting the engine in running positions can be minimized, and a sense of incongruity caused to the driver can be mitigated. That is, if the shift position is a running position, and if a driving force of the engine is directly reflected as a driving force for causing the vehicle to travel, the driver tends to feel unpleasantness. Thus, in such a state, a best possible attempt is made to avoid the starting of the engine. In a neutral position or the like in which the starting of the engine is not reflected as a driving force for the wheels by releasing a clutch or the like, it becomes relatively easy to start the engine.
Further, when the engine is started on the basis of the first starting condition, the controller may set a torque change rate of driven wheels of the vehicle to a predetermined value or less.
This mitigates an abrupt rise in torque of the driven wheels in restarting the engine, namely, an engine starting shock. Consequently, a sense of incongruity caused to the driver is further attenuated.